The invention relates to a process for the preparation of aromatic nitriles by reaction of halogenoaromatics or aryl perfluorosulfonates with alkali metal cyanides in the presence of palladium catalysts, polyethers, and zinc.
The palladium-catalyzed substitution of halogens in aromatic compounds by alkali metal cyanides is disclosed, for example, in U.S. Pat. No. 4,211,721 or T. Okano et al., Synleft, 1998, page 243. The processes described there, however, have the disadvantage that both the yields and the low turnover numbers of the catalysts (TON) of at most 170 make industrial realization uneconomical. An improved process was presented by Maligres et al. in Tetrahedron Letters, 40, 1999, page 8193. However, the cyanide source used is expensive zinc cyanide, which is not acceptable for the industrial scale. The need therefore existed to develop a process that makes possible the palladium catalyzed cyanation of halogenoaromatics or aryl perfluorosulfonates using cheap alkali metal cyanides with high turnover numbers and yields.
There has now been found a process for the preparation of aromatic nitrites of the general formula (I)
Arxe2x80x94[CN]nxe2x80x83xe2x80x83(I)
in which
Ar represents a substituted or unsubstituted aromatic radical, and
n represents one or two,
comprising reacting
(a) an aromatic compound of the general formula (II)
Arxe2x80x94[X]nxe2x80x83xe2x80x83(II)
xe2x80x83in which
Ar and n have the above-mentioned meaning for formula (I), and
X each independently of one another represents chlorine, bromine, iodine, or a perfluoroalkylsulfonyloxy radical,
with
(b) one or more alkali metal cyanides, in the presence of
(c) a palladium catalyst,
(d) zinc, and
(e) one or more polyethers, and
(f) optionally, an aprotic solvent.